The present invention relates to a paper coating material, and a method of manufacturing the same, and more specifically, to a paper coating material which is recyclable and thus environment-friendly, and which has moisture-proof, water-poof, and oil-proof properties, and to a method of manufacturing the same.
In 1907, Houg Moor from the USA invented paper cups and advertised that only disposable cups could ensure the protection of human beings from bacteria. Since then, people have used paper cups over 100 years because paper cups are hygienic and convenient for use.
Paper food containers such as paper cups should be water-proof since the basic role thereof is to put water and a drink therein. Currently, most of paper cups are manufactured by coating or laminating paper with polyethylene (PE). Paper or paper cups coated with polyethylene are excellent in water-proof property and are advantageous for mass production.
However, in reality, there are many problems in recycling paper cups coated with polyethylene instead of disposing the paper cups. That is, in a process of removing polyethylene from the paper cups to be recycled, pulp fiber of paper is damaged and stiffens. Also, in a process of removing polyethylene, it is necessary to separate paper and polyethylene. However, most of polyethylene is not dissociated well in an alkaline solution such as sodium hydroxide, and moreover, it is only partially dissociated even in an alkaline solution at a boiling temperature. When recycling paper having polyethylene not dissociated but still adsorbed thereonto, paper coming out of a papermaking machine sticks to the periphery of a roller when going through a drying process of high temperature. This causes the quality of the paper to be significantly lowered, and therefore, most of the paper can only be recycled as low-quality paper such as toilet paper.
As the demand for environment-friendly paper coating material has grown, there have been many attempts of research and development. Korean Patent No. 10-1089765 discloses a method of manufacturing paper coating material having basic properties, such as water-proof, oil-proof, and heat sealing properties, and an environment-friendly property, by coating copolymer latex having a core-shell structure through a conventional papermaking facility. Since the copolymer latex disclosed above is alkali-dissociable, the recycling possibility is predicted. However, due to the inherent physical properties of copolymer latex, a blocking phenomenon in which paper rolls stick to each other during the manufacturing process at high temperature under high pressure occurs, which makes it difficult to apply to the mass production in the actual papermaking process.
Korean Patent No. 10-1100954 discloses food wrapping paper with an emphasis on environment-friendliness that is produced through a method of coating paper with a coating liquid prepared by mixing a fluorine-based oil-proof agent and polyvinyl alcohol (PVA). However, since polyvinyl alcohol itself is hygroscopic, when the water absorption in food wrapping paper becomes large, the blocking property thereof sharply decreases and the water resistance is deteriorated. Korean Patent 10-1329259 discloses wrapping paper with improved water repellency and oil-proof property by applying, to kraft paper, a coating liquid prepared by mixing starch, paraffin wax emulsion, or polyethylene emulsion. However, moisture permeation over a long period of time could not be prevented.
Paper food containers can be substantially an environment-friendly alternative only if the paper food containers have water-proof, oil-proof, and heat sealing properties and can be readily manufactured even by a conventional papermaking machine. In addition, price competitiveness is essential to replace conventional paper products coated with polyethylene. Environment-friendly paper coating material with such multi-competitiveness has not yet been developed.
Therefore, the present inventor has studied for a long time to solve such a problem and finally developed and completed the present invention through trial and error